1. Field of the Invention
This invention relates to syringes having a retractable needle or cannula and more particularly, to a retractable syringe characterized by a syringe needle which can be retracted into the syringe and locked therein after use to prevent accidental needle sticks or re-use of the syringe. In a preferred embodiment the retractable syringe includes a syringe barrel terminated by a tapered barrel neck which communicates with the syringe barrel interior. As the barrel neck receives the needle hub of the syringe needle, the needle hub is rotated to cause engagement of barrel threads, provided on the inside surface of the barrel neck, with exterior hub threads, provided on the exterior surface of the needle hub, and secure the needle hub in the barrel neck, in confluent relationship with the syringe barrel. A syringe plunger, slidably disposed in the syringe barrel, is terminated by a plunger nipple which is fitted with exterior plunger threads for engaging interior hub threads of the needle hub. After the syringe plunger is operated in conventional fashion to expel the liquid contents of the syringe barrel through the syringe hub and needle, the plunger is rotated in the barrel to threadibly seat the plunger nipple in the needle hub. Because the barrel threads and companion exterior hub threads of the needle hub are oppositely-threaded with respect to the plunger threads and companion interior hub threads, continued rotation of the plunger in the syringe barrel threads the attached needle hub and needle rearwardly from the barrel neck into the syringe barrel interior, by operation of the interior barrel threads and companion exterior hub threads. In a preferred embodiment a plunger lock tip terminates the plunger nipple of the plunger, and seats in a tip receptacle shaped inside the needle hub to further secure the plunger nipple to the needle hub. In a first embodiment of the retractable syringe, a pair of flexible plunger lock tabs is inserted in the plunger shaft, and a locking ridge is shaped circumferentially inside the syringe barrel. After threaded retraction of the contaminated or used needle into the syringe barrel, a pair of plunger lock pins, located in a lock slot provided in the plunger between the plunger lock tabs, are positioned such that the plunger lock tabs are forced outwardly from the plunger and engage the locking ridge to hinder removal of the syringe plunger from the barrel. In a second embodiment a pair of lock plates is provided on the syringe plunger, for engaging the locking ridge and hindering withdrawal of the plunger from the barrel.
Medical treatments frequently include intravenous administration of medications using syringes and needles. Often the syringe needle remains exposed from the time of use until safe disposal of the syringe in a suitable "sharps" container, thus increasing the likelihood of accidental needle sticks during handling of the syringe. With the advent of AIDS and other blood-borne diseases such as hepatitis, the potential risk of accidental needle sticks is attended by dangerous and possibly lethal consequences to health care providers. Accordingly, the retractable syringe of this invention facilitates withdrawal of a used or contaminated syringe needle or cannula into the syringe barrel after use of the syringe in order to reduce exposure of the unprotected needle and minimize the possibility of an accidental needle stick. The retractable syringe further includes a syringe plunger locking mechanism which hinders withdrawal of the syringe plunger and retracted needle from the barrel after use of the syringe, to prevent or discourage re-use of the syringe and reduce the spread of disease resulting from "shared needles".
2. Description of the Prior Art
Syringes having retractable needles are well-known in the art. Typical of these syringes is the "Syringe with Retractable Cannula", detailed in U.S. Pat. No. 4,026,287, dated May 31, 1977, to Irene Haller. The syringe is characterized by a plunger which is slidably disposed in a syringe barrel, and the front end of the plunger can be caused to threadably engage the forward end wall of the syringe barrel by rotating the plunger in the barrel after the fluid contents of the syringe are dispensed. Subsequent retraction of the plunger into the barrel causes the perforated forward end wall of the barrel to break away from the barrel with the plunger, and the cannula, attached to the forward end wall, is retracted into the barrel. U.S. Pat. No. 4,995,874, dated Feb. 26, 1991, to H. Allen Strickland, describes a "Disposable Syringe Device" fitted with a retractable needle. The syringe includes a syringe barrel and a plunger in which a threaded extension or threadlock, provided on the forward end of the plunger, is capable of engaging a threadbare element, provided in the forward neck portion of the barrel, by rotating the plunger in the barrel after the fluid contents of the syringe are dispensed from the barrel. Because the threadbore element is secured to the needle, the needle may be withdrawn into the barrel by pulling the plunger rearwardly in the barreL A "Syringe" is disclosed in U.S. Pat. No. 5,141,495, dated Aug. 25, 1992, to Gudmar Olovson. The syringe is characterized by a syringe barrel, within which is slidably disposed a plunger terminated by a plunger piston. The plunger is provided with two sets of right-handed threads which rotate the plunger in the clockwise direction as the plunger is extended from the barrel and in the counterclockwise direction as the plunger is extended into the barrel. The plunger piston is attached to the plunger by means of left-handed threads, such that extension of the plunger from the barrel tightens the plunger piston on the plunger, whereas extension of the plunger into the barrel unthreads the plunger piston from the plunger. A set of lock tabs extends from the barrel walls into the barrel, at the needle end of the barrel for engaging the unthreaded plunger piston. As the plunger is extended into the barrel to expel the liquid syringe contents through the needle, the plunger piston becomes unthreaded from the plunger and is permanently seated in the needle end of the piston by means of the lock tabs, preventing re-use of the syringe. U.S. Pat. No. 5,417,661, dated May 23, 1995, to Jeffrey L. Stringer, et aL, describes a "Safety Syringe", characterized by a disposable safety hypodermic syringe wherein the used syringe needle is retracted into the syringe barrel by rotating the syringe plunger, and the needle is captured completely within the barrel when the plunger is retracted and locked with respect to the barrel. U.S. Pat. No. 5,533,970, dated Jul. 9, 1996, to Howard S. Berger, et al., details a "Retractable Needle Syringe" including a barrel having open front and rear ends. An elongated plunger, slidably disposed in the barrel includes a radially-extending plunger lock tab adjacent to its insertion end. A needle carrier is slidably disposed in the barrel interior at the front end thereof, and a needle cannula extends forwardly from the needle carrier, in fluid communication with the barrel interior and through the open front end of the barrel. The proximal end of the carrier includes an open-ended groove which is sized and shaped to receive the plunger lock tab. Rotation of the plunger inside the barrel causes the lock tab to enter the groove, thereby connecting the plunger with the carrier. After use of the syringe, the plunger can be extended from the syringe barrel to slide the carrier away from the front end of the barrel and retract the needle into the barrel. An "Ampule Safety Syringe" is detailed in U.S. Pat. No. 5,593,391, dated Jan. 14, 1997, to Sydney D. Stanners. The syringe is characterized by a syringe ampule or barrel having a finger grip provided on the rear end of the barrel and an elongated plunger, terminated by a plunger piston, slidably disposed in the barrel and extending through an opening provided in the finger grip. A barrel cap is affixed to the front end of the barrel, and a hollow needle extends through a needle hub which is threaded in the barrel cap. After the liquid contents of the barrel are expelled through the needle by operation of the plunger, the plunger piston engages the needle, and extension of the plunger from the barrel causes the plunger piston to draw or retract the needle into the barrel.
An object of this invention is to provide a syringe having a syringe needle which is capable of being retracted into the syringe after use.
Another object of this invention is to provide a syringe having a cannulated syringe needle which can be retracted and locked in the syringe after use in order to prevent accidental needle sticks and re-use of the syringe.
Still another object of this invention is to provide a syringe characterized by a syringe barrel, a cannulated syringe needle terminating the syringe barrel and a syringe plunger slidably disposed in the syringe barrel for expelling the liquid contents of the barrel through the needle, wherein the needle can be retracted into the barrel after use by rotating the plunger in the barrel thereby causing the plunger to first threadibly engage and seat the syringe needle and then thread the needle into the barrel as rotation of the plunger is continued.
Yet another object of this invention is to provide a syringe characterized by a syringe barrel; a cannulated syringe needle terminating the syringe barrel; and a syringe plunger slidably disposed in the syringe barrel for expelling the liquid contents of the syringe from the syringe barrel through the needle, which needle can be retracted into the barrel after use of the syringe by initially rotating the plunger in the barrel and causing the plunger to threadibly engage and seat the syringe needle, and then incrementally threadibly drawing or retracting the needle into the barrel by continued rotation of the plunger; and a pair of flexible plunger lock tabs provided on the plunger is expanded outwardly from the plunger and caused to engage a locking ridge shaped circumferentially in the plunger barrel, by a pair of plunger lock pins located in a lock slot provided in the plunger between the plunger lock tabs, thereby substantially locking the retracted needle inside the syringe barrel and preventing or hindering removal of the plunger and attached needle from the barrel.
A still further object of this invention is to provide a syringe characterized by a syringe barrel; a cannulated syringe needle terminating the syringe barrel; and a syringe plunger sidably disposed in the syringe barrel for expelling the liquid contents of the syringe from the syringe barrel through the needle, which needle can be retracted into the barrel after use of the syringe by initially rotating the plunger in the syringe barrel and causing the plunger to threadibly engage and seat the syringe needle, and then incrementally threading the needle into the barrel by continued rotation of the plunger; and at least one plunger lock plate provided on the plunger for engaging a locking ridge shaped circumferentially inside the syringe barrel, thereby substantially locking the retracted needle inside the barrel and preventing or hindering removal of the plunger and attached needle from the barreL